Objective To determine whether blood type affects the risk of thromboembolic complications in patients with atrial fibrillation (AF). Patients and Methods The Mayo Clinic electronic medical record was searched (between January 1, 2004, and December 31, 2010) to identify all patients with AF with blood group assessment. Records were analyzed for stroke, transient ischemic attack, left atrium appendage thrombus, cerebral or peripheral embolism, and hemorrhagic stroke. All events were adjusted for Congestive heart failure, Hypertension, Age >75 Years, Diabetes mellitus, and Stroke/transient ischemic attack score. Results Of the 47,816 patients with AF, 14,462 had blood group type available (40% women; mean age, 73±12 years). These included 12,363 patients with nonvalvular atrial fibrillation (NVAF) (40% women; mean age, 73±12 years) and 2099 patients with valvular AF (41% women, mean age, 73±12 years). Within patients with NVAF, the rate of peripheral embolization was significantly lower in those with blood type O (2.0%) than in those with other blood types (3.0%; odds ratio, 0.66; 95% CI, 0.52-0.84; P<.001). Neither cerebral thromboembolic (8.1% for "O" vs 8.2% for "non-O" blood group for NVAF and 7.29% vs 7.76% for valvular AF) nor cerebral hemorrhage (2.0% each group) events rates differed by blood group. Conclusion Blood group O may be protective against peripheral cardioembolic complications of NVAF, which may relate, in part, to reduced circulating von Willebrand factor levels. Cerebral thromboembolic event rates did not differ by blood group.
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